This invention concerns a method of manufacturing anti-falsification paper. More specifically, it relates to a method of manufacturing anti-falsification paper which is so-called xe2x80x9cthread-inserted, window paperxe2x80x9d in which a thread is intermittently exposed to the surface of paper.
Various anti-falsification countermeasures have been applied, for example, to bank notes and gift cards so that they can not be illegally modified or forged. One of the concepts for the anti-falsification countermeasures is to manufacture paper by using a manufacturing technique at such a high level to make manufacture not easy. As an example, there is anti-falsification paper referred to as xe2x80x9cthread-inserted, window paperxe2x80x9d, which have been used generally for bank notes in many countries. FIG. 7 shows an example. FIG. 7 is an example of anti-falsification paper in which windows W are arranged each at a predetermined distance in right and left two rows in the machining direction of the paper upon manufacture thereof and a thread T is exposed intermittently in the windows.
Various manufacturing methods have been proposed for the thread-inserted, window paper. For example, Japanese Patent Publication No. 5-085680/1993 proposes a method of manufacturing thread-inserted, window paper by immersing a belt mechanism, which has a groove with a thread being passed through the top end of a protrusion of a guide of a convex/concave shape, in a liquid paper stock suspension on wire cloth.
Further, Japanese Patent Laid-Open No. 6-272200/1994 proposes a method of installing a pressurized air nozzle in a rotary drum disposed on wire cloth in a Fourdrinier paper machine and intermittently blowing off the pulp slurry deposited on the thread previously embedded into wet paper with pressurized air thereby exposing the thread.
Further, U.S. Pat. No. 4,462,866 proposes a method of using a wire mesh having raised portions as a face wire of a cylinder paper machine and incorporating a thread while bringing it into contact with the raised portions on the surface of the wire mesh thereby inserting and exposing the thread in windows.
The method of manufacturing the thread-inserted, window paper proposed by Japanese Patent Publication No. 5-085680/1993 involves problems in that the apparatus is complicated, contours of the windows become obscure if the drained condition of the paper stock on the wire cloth fluctuates even slightly, the thread can not clearly be recognized visually or it is extremely difficult to keep the belt horizontal relative to the paper machine since the belt expands outwardly by a centrifugal force during operation, failing to stably insert the thread.
Further, the thread-inserted, window paper proposed in Japanese Patent Laid-Open No. 6-272200/1994 involves a problem that since pressurized air blows off the paper slurry in an unnecessarily excessive amount, the formation at that portion is deteriorated and, on the other hand, when the pneumatic pressure of pressurized air is lowered for preventing this, portions in which the thread is not exposed to the surface of water mark portions are increased, which also making it impossible to clearly recognize the thread visually.
Further, the thread-inserted, window paper proposed in U.S. Pat. No. 4,462,866 involves a problem that the contours of the windows becomes obscure since the window is formed by fabricating the wire mesh into a shape having raised portions and. thus the thread can not clearly be observed visually. Further, when different kinds of thread-inserted, window paper are intended to be manufactured, since the cylinder face wire has to be replaced after once stopping the paper machine, it results in a problem that the cost is increased in the manufacture of small lot paper.
This invention has an object to solve the problems in the prior art described above. Specifically, it intends to provide a novel method of manufacturing thread-inserted, window paper, capable of shortening the stopping period of a paper machine even for the manufacture of different kinds of paper by a relatively simple apparatus, the resulting paper having windows of clear contours, thread being exposed surely at the window portions and the exposed thread being clearly recognizable visually.
A gist of this invention resides in a method of manufacturing anti-falsification paper, which comprises guiding wet paper in which a thread is embedded in a paper layer while being in intimate contact with a center roll having protrusions arranged on the surface thereof intermittently at a predetermined distance, frictionally rubbing the surface of the wet paper on the protrusions by a friction roll thereby moving fibers at the surface of the wet paper on the protrusions to form exposed portions of the thread intermittently on the surface of the wet paper and then drying the same.